Hermetically sealed micro-device package using cold-gas dynamic spray material deposition

ABSTRACT

A method for manufacturing a cover assembly including a transparent window portion and a metallic frame that can be joined to a micro-device package base to form a hermetically sealed micro-device package. A sheet of a transparent material is provided having a window portion defined thereupon, the window portion having finished top and bottom surfaces. A frame-attachment area is prepared on the sheet, the frame-attachment area circumscribing the window portion. A first quantity of powdered metal particles is sprayed onto the prepared frame-attachment area of the sheet using a jet of gas, the gas being at a temperature below the fusing temperature of the metal particles. The jet of gas has a velocity sufficient to cause the metal particles to merge with one another upon impact with the sheet and with one another so as to form an initial continuous metallic coating adhering to the frame-attachment area of the sheet. Successive quantities of powdered metal particles are applied over the initial continuous metallic coating using the jet of gas so as to form a continuous built-up metallic frame incorporating the initial continuous metallic coating as its base and having an overall thickness that is a predetermined thickness.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-In-Part of pending U.S. patentapplication Ser. No. 10/104,315 (Atty. Dkt. No. STRK-25,911) filed Mar.22, 2002 and titled “HERMETICALLY SEALED MICRO-DEVICE PACKAGE WITHWINDOW.”

TECHNICAL FIELD OF THE INVENTION

[0002] The current invention relates to packages for photonic devices,optical devices, micro-mechanical devices, micro-electromechanicalsystems (MEMS) devices or micro-optoelectromechanical systems (MOEMS)devices, and more particularly, to methods for manufacturing packageshaving a hermetically sealed chamber covered by a transparent windowusing cold-gas dynamic spray material deposition.

BACKGROUND OF THE INVENTION

[0003] Photonic, optical and micro-mechanical devices are typicallypackaged such that the active elements (i.e., the emitters, receivers,micro-mirrors, etc.) are disposed within a sealed chamber to protectthem from handling and other environmental hazards. In many cases, it ispreferred that the chamber be hermetically sealed to prevent the influx,egress or exchange of gasses between the chamber and the environment. Ofcourse, a window must be provided to allow light or otherelectromagnetic energy of the desired wavelength to enter and/or leavethe package. In some cases, the window will be visibly transparent, e.g.if visible light is involved, but in other cases the window may bevisibly opaque while still being “optically” transparent toelectromagnetic energy of the desired wavelengths. In many cases, thewindow is given certain optical properties to enhance the performance ofthe device. For example, a glass window may be ground and polished toachieve certain flatness specifications in order to avoid distorting thelight passing therethrough. In other cases, anti-reflective oranti-refractive coatings may be applied to the window to improve lighttransmission therethrough.

[0004] Hermetically sealed micro-device packages with windows haveheretofore been produced using cover assemblies with metal frames andglass window panes. To achieve the required hermetic seal, the glasswindow pane has heretofore been fused to its metallic frame by heatingit in a furnace at a temperature exceeding the glass transitiontemperature, T_(G) (typically at or above 900° C.). However, because thefusing temperature is above T_(G), the original surface finish of theglass pane is typically ruined, making it necessary to finish orre-finish (e.g., grinding and polishing) both surfaces of the windowpane after fusing in order to obtain the necessary opticalcharacteristics. This polishing of the window panes requires additionalprocess steps during manufacture of the cover assemblies, which stepstend to be relatively time and labor intensive, thus addingsignificantly to the cost of the cover assembly, and hence to the costof the overall package. In addition, the need to polish both sides ofthe glass after fusing requires the glass to project both above andbelow the attached frame. This restricts the design options for thecover assembly with respect to glass thickness, dimensions, etc., whichcan also result in increased material costs.

[0005] Once a cover assembly with a hermetically sealed window isprepared, it is typically seam welded to the device base (i.e.,substrate) in order to produce the finished hermetically sealed package.Seam welding uses a precisely applied AC current to produce localizedtemperatures of about 1,100° C. at the frame/base junction, therebywelding the metallic cover assembly to the package base and forming ahermetic seal. To prevent distortion of the glass windowpane or package,the metal frame of the cover assembly should be fabricated from Kovaralloy or another alloy having a CTE (i.e., coefficient of thermalexpansion) which is similar to that of the transparent window materialand to the CTE of the package base.

[0006] While the methods described above have heretofore produceduseable window assemblies for hermetically sealed micro-device packages,the relatively high cost of these window assemblies is a significantobstacle to their widespread application. A need therefore exists, forpackage and component designs and assembly methods which reduce thelabor costs associated with producing each package.

[0007] A need still further exists for package and component designs andassembly methods which will minimize the manufacturing cycle timerequired to produce a completed package.

[0008] A need still further exists for package and component designs andassembly methods which reduce the number of process steps required forthe production of each package. It will be appreciated that reducing thenumber of process steps will reduce the overhead/floor space required inthe production facility, the amount of capital equipment necessary formanufacturing, and handling costs associated with transferring the workpieces between various steps in the process. A reduction in the cost oflabor may also result. Such reductions would, of course, further reducethe cost of producing these hermetic packages.

[0009] A need still further exists for package and component designs andassembly methods which will reduce the overall materials costsassociated with each package, either by reducing the initial materialcost, by reducing the amount of wastage or loss during production, orboth.

SUMMARY OF THE INVENTION

[0010] The present invention disclosed and claimed herein comprises, inone aspect thereof, a method for manufacturing a cover assemblyincluding a transparent window portion and a metallic frame that can bejoined to a micro-device package base to form a hermetically sealedmicro-device package. A sheet of a transparent material is providedhaving a window portion defined thereupon, the window portion havingfinished top and bottom surfaces. A frame-attachment area is prepared onthe sheet, the frame-attachment area circumscribing the window portion.A first quantity of powdered metal particles is sprayed onto theprepared frame-attachment area of the sheet using a jet of gas, the gasbeing at a temperature below the fusing temperature of the metalparticles. The jet of gas has a velocity sufficient to cause the metalparticles to merge with one another upon impact with the sheet and withone another so as to form an initial continuous metallic coatingadhering to the frame-attachment area of the sheet. Successivequantities of powdered metal particles are applied over the initialcontinuous metallic coating using the jet of gas so as to form acontinuous built-up metallic frame incorporating the initial continuousmetallic coating as its base and having an overall thickness that is apredetermined thickness.

[0011] The present invention disclosed and claimed herein comprises, inanother aspect thereof, a method for manufacturing a cover assembly fora micro-device package. A sheet of a transparent material is providedhaving a window portion defined thereupon. A first quantity of powderedparticles is sprayed onto the sheet using a jet of gas, the gas being ata temperature below the fusing temperature of the particles. The jet ofgas has a velocity sufficient to cause the particles to merge with oneanother upon impact with the sheet and with one another so as to form aninitial continuous coating adhering to the sheet and circumscribing thewindow portion thereof. Successive quantities of powdered particles areapplied over the initial continuous coating using the jet of gas so asto form a continuous built-up frame circumscribing the window portionand incorporating the initial continuous coating.

[0012] The present invention disclosed and claimed herein comprises, inyet another aspect thereof, a cover assembly that can be welded to amicro-device package base to form a hermetically sealed micro-devicepackage. The cover assembly includes a sheet of a transparent materialhaving a window portion defined thereupon. A built-up metallic frameadheres to the sheet and circumscribes the window portion, the framehaving been deposited onto the sheet as follows: First, a first quantityof powdered metal particles is sprayed onto a prepared frame-attachmentarea of the sheet using a jet of gas, the gas being at a temperaturebelow the fusing temperature of the metal particles, and the jet of gashaving a velocity sufficient to cause the metal particles to merge withone another upon impact with the sheet and with one another so as toform an initial continuous metallic coating adhering to theframe-attachment area of the sheet. Next, successive quantities ofpowdered metal particles are applied over the initial continuousmetallic coating using the jet of gas so as to form the built-upmetallic frame incorporating the initial continuous metallic coating asits base and having an overall thickness that is a predeterminedthickness.

[0013] The present invention disclosed and claimed herein comprises, instill another aspect thereof, a micro-device module including a packagebase, a micro-device supported on the package base, and a cover assemblyjoined to the package base so as to encapsulate the micro-device in ahermetically sealed cavity formed between the cover assembly and thepackage base. The cover assembly including a sheet of a transparentmaterial having a window portion defined thereupon and a built-upmetallic frame adhering to the sheet and circumscribing the windowportion, the frame having been deposited onto the sheet as follows:First, a first quantity of powdered metal particles is sprayed onto thesheet using a jet of gas, the gas being at a temperature below thefusing temperature of the metal particles, and the jet of gas having avelocity sufficient to cause the metal particles to merge with oneanother upon impact with the sheet and with one another so as to form aninitial continuous metallic coating adhering to the sheet. Next,successive quantities of powdered metal particles are applied over theinitial continuous metallic coating using the jet of gas so as to formthe built-up metallic frame incorporating the initial continuousmetallic coating as its base.

[0014] The present invention disclosed and claimed herein comprises, inyet another aspect thereof, a method for manufacturing a cover assemblyincluding a transparent window portion and a frame that can be joined toa micro-device package base to form a hermetically sealed micro-devicepackage. First a sheet of a transparent material is provided having awindow portion defined thereupon. A frame-attachment area is prepared onthe sheet, the frame-attachment area circumscribing the window portion.Next, metal is deposited onto the prepared frame-attachment area of thesheet using cold-gas dynamic spray deposition until a built-up metalframe is formed on the sheet having a predetermined thickness above theframe-attachment area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a hermetically sealed micro-devicepackage;

[0016]FIG. 2 is a cross-sectional view of the micro-device package ofFIG. 1;

[0017]FIG. 3 is an exploded view of a cover assembly manufactured inaccordance with one embodiment of the current invention;

[0018]FIGS. 4a and 4 b show transparent sheets having contoured sides,specifically:

[0019]FIG. 4a showing a sheet having both sides contoured;

[0020]FIG. 4b showing a sheet having one side contoured;

[0021]FIG. 5 shows an enlarged view of the sheet seal-ring area prior tometallization;

[0022]FIG. 6 shows an enlarged view of the sheet seal-ring area aftermetallization;

[0023]FIG. 7 shows a cross-sectional view through a pre-fabricatedframe;

[0024]FIG. 8 illustrates placing the frame against the metallized sheetprior to bonding;

[0025]FIG. 9 is a block diagram of a process for manufacturing coverassemblies using prefabricated frames in accordance with one embodiment;

[0026]FIG. 10 is an exploded view of a cover assembly manufactured usinga solder preform;

[0027]FIG. 11 is a partial perspective view of another embodimentutilizing solder applied by inkjet;

[0028]FIGS. 12a-c and FIGS. 13a-c illustrate a process of manufacturingcover assemblies in accordance with yet another embodiment of theinvention, specifically:

[0029]FIG. 12a shows the initial transparent sheet;

[0030]FIG. 12b shows the transparent sheet after initial metallization;

[0031]FIG. 12c shows the transparent sheet after deposition of theintegral frame/heat spreader;

[0032]FIG. 13a shows a partial cross-section of the sheet of FIG. 12a;

[0033]FIG. 13b shows a partial cross-section of the sheet of FIG. 12b;

[0034]FIG. 13c shows a partial cross-section of the sheet of FIG. 12c;

[0035]FIG. 14 is a block diagram of a process for manufacturing coverassemblies using cold gas dynamic spray technology in accordance withanother embodiment;

[0036]FIGS. 15a-15 b illustrate a multi-unit assembly manufactured inaccordance with another embodiment; specifically:

[0037]FIG. 15a illustrates an exploded view of a the multi-unitassembly;

[0038]FIG. 15b is bottom view of the frame of FIG. 15a;

[0039]FIG. 16a illustrates compliant tooling formed in accordance withanother embodiment;

[0040]FIG. 16b is a side view of a multi-unit assembly illustrating themethod of separation;

[0041]FIGS. 17a and 17 b illustrate the manufacture of multiple coverassemblies in accordance with yet another embodiment, specifically:

[0042]FIG. 17a shows the transparent sheet in its original state;

[0043]FIG. 17b illustrates the sheet after deposition of themulti-aperture frame/heat spreader;

[0044]FIGS. 18a-18 c illustrate an assembly configuration suitable foruse with electrical resistance heating; specifically:

[0045]FIG. 18a illustrates the configuration of the sheet;

[0046]FIG. 18b illustrates the configuration of the frame;

[0047]FIG. 18c illustrates the joined sheet and frame; and

[0048]FIGS. 19a-19 f illustrate multi-unit assembly configurationssuitable for heating with electrical resistance heating.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

[0049] Referring now to FIGS. 1 and 2, there is illustrated a typicalhermetically sealed micro-device package for housing photonic devices,optical devices (i.e., including reflective, refractive and diffractivetype devices), micro-optoelectromechanical systems (i.e., MOEMS) devicesand micro-electromechanical systems (i.e., MEMs) devices. The package102 comprises a base or substrate 104 which is hermetically sealed to acover assembly 106 comprising a frame 108 and a transparent window 110.A micro-device 112 mounted on the base 104 is encapsulated within acavity 114 when the cover assembly 106 is joined to the base 104. One ormore electrical leads 116 may pass through the base 104 to carry power,ground, and signals to and from the micro-device 112 inside the package102. It will be appreciated that the electrical leads 116 must also behermetically sealed to maintain the integrity of the package 102. Thewindow 110 is formed of an optically or electro-magnetically transparentmaterial. For purposes of this application, the term “transparent”refers to materials which allow the transmission of electromagneticradiation having predetermined wavelengths, including, but not limitedto, visible light, infrared light, ultraviolet light, microwaves, radiowaves, or x-rays. The frame 108 is formed from a material, typically ametal alloy, which preferably has a CTE close to that of both the window110 and the package base 104.

[0050] Referring now to FIG. 3, there is illustrated an exploded view ofa cover assembly manufactured in accordance with one embodiment of thecurrent invention. The cover assembly 300 includes a frame 302 and asheet 304 of a transparent material. The frame 302 has a continuoussidewall 306 which defines a frame aperture 308 passing therethrough.The frame sidewall 306 includes a frame seal-ring area 310 (denoted bycrosshatching) circumscribing the frame aperture 308. Since the frame302 will eventually be welded to the package base 104, it is usuallyformed of a weldable metal or alloy, preferably one having a CTE veryclose to that of the micro-device package base 104. In some embodiments,however, the cover assembly frame 304 may be formed of a non-metallicmaterial such as ceramic or alumina. Regardless of whether the frame 302is formed of a metallic or non-metallic material, the surface of theframe seal-ring area 310 must be metallic (e.g., metal plated if notsolid metal) to facilitate the hermetic sealing of the sheet 304 to theframe. In a preferred embodiment, the frame is primarily formed of analloy having a nominal chemical composition of 54% iron (Fe), 29% nickel(Ni) and 17% cobalt (Co). Such alloys are also known by the designationASTM F-15 alloy and by the trade name Kovar Alloy. As used in thisapplication, the term “Kovar Alloy” will be understood to mean the alloyhaving the chemical composition just described. In embodiments where aKovar Alloy frame 302 is used, it is preferred that the surface of theframe seal-ring area 310 have a surface layer of gold (Au) overlying alayer of nickel (Ni). The frame 302 also includes a base seal area 320which is adapted for eventual joining, typically by welding, to thepackage base 104. The base seal area 320 frequently includes a layer ofnickel overlaid by a layer of gold to facilitate seam welding to thepackage base. Although the gold over nickel surface layers are onlyrequired along the base seal-ring area 320, it will be appreciated thatin many cases, for example, where solution bath plating is used to applythe surface materials, the gold over nickel layers may be applied to theentire surface of the frame 302. The sheet 304 can be any type oftransparent material, for example, soft glass (e.g., soda-lime glass),hard glass (e.g. borosilicate glass), crystalline materials such asquartz and sapphire, or polymeric materials such as polycarbonateplastic. As previously discussed, it is preferred that the material ofthe sheet 304 have a CTE that is similar to that of the frame 304 and ofthe package base 104 to which the cover assembly will eventually beattached. For many semiconductor photonic, MEMS or MOEMS applications, aborosilicate glass is well suited for the material of the sheet 304.Examples of suitable glasses include Corning 7052, 7050, 7055, 7056,7058, 7062, Kimble (Owens Corning) EN-1, and Kimble K650 and K704. Othersuitable glasses include Abrisa soda-lime glass, Schott 8245 and OharaCorporation S-LAM60.

[0051] The sheet 304 has a window portion 312 defined thereupon, i.e.,this is the portion of the sheet 302 which must remain transparent toallow for the proper functioning of the encapsulated, i.e., packaged,micro-device 112. The window portion 312 of the sheet has top and bottomsurfaces 314 and 316, respectively, that are optically finished in thepreferred embodiment. The sheet 304 is preferably obtained with the topand bottom surfaces 314 and 316 of the window portion 312 in ready touse form, however, if necessary the material may be ground and polishedor otherwise shaped to the desired surface contour and finish as apreliminary step of the manufacturing process. While in many cases thewindow portion 312 will have top and bottom surfaces of 314 and 316 thatare optically flat and parallel to one another, it will be appreciatedthat in other embodiments at least one of the finished surfaces of thewindow portion will be contoured. A sheet seal-ring area 318 (denotedwith cross-hatching) circumscribes the window portion 312 of the sheet304, and provides a suitable surface for joining to the front seal-ringarea 310.

[0052] Referring now to FIGS. 4a and 4 b, there are illustratedtransparent sheets having contoured sides. In FIG. 4a, transparent sheet304′ has both a curved top side 314′ and a curved bottom side 316′producing a window portion 312 having a curved contour with a constantthickness. In FIG. 4b, sheet 304″ has a top side 314″ which is curvedand a bottom side 316″ which is flat, thereby resulting in a windowportion 312 having a plano-convex lens arrangement. It will beappreciated that in similar fashion (not illustrated) the finishedsurfaces 314 and 316 of the window portion 312 can have theconfiguration of a refractive lens including a plano-convex lens aspreviously illustrated, a double convex lens, a plano-concave lens or adouble concave lens. Other surface contours may give the finishedsurfaces of the window portion 312 the configuration of a Fresnel lensor of a diffraction grating, i.e., “a diffractive lens.”

[0053] In many applications, it is desirable that window portion 312 ofthe sheet 304 have enhanced optical or physical properties. To achievethese properties, surface treatments or coatings may be applied to thesheet 304 prior to or during the assembly process. For example, thesheet 304 may be treated with siliconoxynitride (SiOn) to provide aharder surface on the window material. Whether or not treated with SiOn,the sheet 304 may be coated with a scratch resistant/abrasion resistantmaterial such as amorphous diamond-like carbon (DLC) such as that soldby Diamonex, Inc., under the name Diamond Shield®. Other coatings whichmay be applied in addition to, or instead of, the SiOn or diamond-likecarbon include, but are not limited to, optical coatings,anti-reflective coatings, refractive coatings, achromatic coatings,optical filters, electromagnetic interference (EMI) and radio frequency(RF) filters of the type known for use on lenses, windows and otheroptical elements. It will be appreciated that the optical coatingsand/or surface treatments can be applied either on the top surface 314or the bottom surface 316, or in combination on both surfaces, of thewindow portion 312. It will be further appreciated, that the opticalcoatings and treatments just described are not illustrated in thefigures due to their transparent nature.

[0054] In some applications, a visible aperture is formed around thewindow portion 312 of the sheet 304 by first depositing a layer ofnon-transparent material, e.g., chromium (Cr), over the entire surfaceof the sheet and then etching the non-transparent material from thedesired aperture area. This procedure provides a sharply defined borderto the window portion 312 which is desirable in some applications. Thisoperation may be performed prior to or after the application of othertreatments depending on the compatibility and processing economics.

[0055] The next step of the process of manufacturing the cover assembly300 is to prepare the sheet seal-ring area 318 for metallization. Thesheet seal-ring area 318 circumscribes the window portion 312 of thesheet 304, and for single aperture covers is typically disposed aboutthe perimeter of the bottom surface 316. It will be appreciated,however, that in some embodiments the sheet seal-ring area 318 can belocated in the interior portion of a sheet, for example where the sheetwill be diced to form multiple cover assemblies (i.e., as describedlater herein). The sheet seal-ring area 318 generally has aconfiguration which closely matches the configuration of the frameseal-ring area 310 to which it will eventually be joined. At a minimum,preparing the sheet seal-ring area 318 involves a thorough cleaning toremove any greases, oils or other contaminants from the surface. Morecommonly, preparing the sheet seal-ring area 318 involves roughening theseal-ring area by chemical etching, laser ablating, mechanical grindingor sandblasting this area. This roughening increases the surface area ofthe sheet seal-ring, thereby providing increased adhesion for thesubsequently deposited metallization materials.

[0056] Referring now to FIG. 5, there is illustrated a portion of thesheet 304 which has been placed bottom side up to better illustrate thepreparation of the sheet seal-ring area 318. In this example theseal-ring area 318 has been given a roughened surface 501 to improveadhesion of the metallic layers to be applied. Chemical etching toroughen glass and similar transparent materials is well known.Alternatively, laser ablating, conventional mechanical grinding orsandblasting may be used. A grinding wheel with 325 grit is believedsuitable for most glass materials, while a diamond grinding wheel may beused for sapphire and other hardened materials. The depth 502 to whichthe roughened surface 501 of the sheet seal-ring area 318 penetrates thesheet 304 is dependent on at least two factors: first, the desiredmounting height of the bottom surface 316 of the window relative to thepackage bottom and/or the micro-device 112 mounted inside the package;and second, the required thickness of the frame 306 including all of thedeposited metal layers (described below). It is believed that etching orgrinding the sheet seal-ring area 318 to a depth of 502 within the rangefrom about 0 inches to about 0.05 inches will provide a satisfactoryadhesion for the metallized layers as well as providing an easilydetectable “lip” for locating the sheet 304 in the proper positionagainst the frame 306 during subsequent joining operations.

[0057] It will be appreciated that it may be necessary or desirable toprotect the finished surfaces 314 and/or 316 in the window portion 312of the sheet (e.g., the portions that will be optically active in thefinished cover assembly) from damage during the roughening process. Ifso, the surfaces 314 and/or 316 may be covered with semiconductor-grade“tacky tape” or other known masking materials prior to roughening. Themask material must, of course, be removed in areas where theetching/grinding will take place. Sandblasting is probably the mosteconomical method of selectively removing strips of tape or maskingmaterial in the regions that will be roughened. If sandblasting is used,it could simultaneously perform the tape removal operation and theroughening of the underlying sheet.

[0058] Referring now to FIG. 6, there is illustrated a view of theseal-ring area 318 of the sheet 304 after metallization. The next stepof the manufacturing process is to apply one or more metallic layers tothe prepared sheet seal-ring area 318. The current inventioncontemplates several options for accomplishing this metallization. Afirst option is to apply metal layers to the sheet seal-ring area 318using conventional chemical vapor deposition (CVD) technology. CVDtechnology includes atmospheric pressure chemical vapor deposition(APCVD), low pressure chemical vapor deposition (LPCVD), plasma assisted(enhanced) chemical vapor deposition (PACVD, PECVD), photochemical vapordeposition (PCVD), laser chemical vapor deposition (LCVD), metal-organicchemical vapor deposition (MOCVD) and chemical beam epitaxy (CBE). Asecond option for metallizing the roughened seal-ring area 318 is usingphysical vapor deposition (PVD) technology. PVD technology includessputtering, ion plasma assist, thermal evaporation, vacuum evaporation,and molecular beam epitaxy (MBE). A third option for metallizing theroughened sheet seal-ring area 318 is using solution bath platingtechnology (SBP). Solution bath plating includes electroplating,electroless plating and electrolytic plating technology. While solutionbath plating cannot be used for depositing the initial metal layer ontoa nonmetallic surface such as glass or plastic, it can be used fordepositing subsequent layers of metal or metal alloy to the initiallayer. Further, it is envisioned that in many cases, solution bathplating will be the most cost effective metal deposition technique.Since the use of chemical vapor deposition, physical vapor depositionand solution bath plating to deposit metals and metal alloys is wellknown, these techniques will not be further described herein.

[0059] A fourth option for metallizing the sheet seal-ring area 318 ofthe sheet 304 is so-called cold-gas dynamic spray technology, also knownas “cold-spray”. This technology involves the spraying of powderedmetals, alloys, or mixtures of metal and alloys onto an article using ajet of high velocity gas to form continuous metallic coating attemperatures well below the fusing temperatures of the powderedmaterial. Details of the cold-gas dynamic spray deposition technologyare disclosed in U.S. Pat. No. 5,302,414 to Alkhimov et al. It has beendetermined that aluminum provides good results when applied to glassusing the cold-gas dynamic spray deposition. The aluminum layer adheresextremely well to the glass and may create a chemical bond in the formof aluminum silicate. However, other materials may also be applied as afirst layer using cold-spray, including tin, zinc, silver and gold.Since the cold-gas dynamic spray technology can be used at lowtemperatures (e.g., near room temperature), it is suitable formetallizing materials having a relatively low melting point, such aspolycarbonates or other plastics, as well as for metallizingconventional materials such as glass, alumina, and ceramics.

[0060] For the initial metallic layer deposited on the sheet 304, it isbelieved that any of chromium, nickel, aluminum, tin, tin-bismuth alloy,gold, gold-tin alloy can be used, this list being given in order ofincreasing adhesion to glass. Any of these materials can be applied tothe sheet seal-ring area 318 using any of the CVD or PVD technologies(e.g., sputtering) previously described. After the initial layer 602 isdeposited onto the sheet seal-ring area 318 of the nonmetallic sheet304, additional metal layers, e.g., second layer 604, third layer 606and fourth layer 608 (as applicable) can be added by any of thedeposition methods previously described, including solution bathplating. It is believed that the application of the following rules willresult in satisfactory thicknesses for the various metal layers. RuleNo. 1: the minimum thickness, except for the aluminum or tin-basedmetals or alloys which will be bonded to the gold-plated Kovar alloyframe: 0.002 microns. Rule 2: the minimum thickness for aluminum ortin-based metals or alloys deposited onto the sheet or as the finallayer, which will be bonded to the gold-plated Kovar alloy frame: 0.8microns. Rule 3: the maximum thickness for aluminum or tin-based metalsor alloys deposited onto the sheet or as the final layer, which will bebonded to the gold-plated Kovar alloy frame: 63.5 microns. Rule 4: themaximum thickness for metals, other than chromium, deposited onto thesheet as the first layer and which will have other metals or alloysdeposited on top of them: 25 microns. Rule 5: the maximum thickness formetals, other than chromium, deposited onto other metals or alloys asintermediate layers: 6.35 microns. Rule 6: the minimum thickness formetals or alloys deposited onto the sheet or as the final layer, whichwill act as the solder for attachment to the gold-plated Kovar alloyframe: 7.62 microns. Rule 7: the maximum thickness for metals or alloysdeposited onto the sheet or as the final layer, which will act as thesolder for attachment to the gold-plated Kovar alloy frame: 101.6microns. Rule 8: the maximum thickness for chromium: 0.25 microns. Rule9: the minimum thickness for gold-tin solder, applied via inkjet orsupplied as a solder preform: 6 microns. Rule 10: the maximum thicknessfor gold-tin solder, applied via inkjet or supplied as a solder preform:101.6 microns. Rule 11: The minimum thickness for immersion zinc; 0.889microns. Note that the above rules apply to metals deposited using alldeposition methods other than cold-gas dynamic spray deposition.

[0061] For cold spray applications, the following rules apply: Rule 1:the minimum practical thickness for any metal layer: 2.54 microns. Rule2: the maximum practical thickness for the first layer, and alladditional layers, but not including the final Kovar alloy layer: 127microns. Rule 3: the maximum practical thickness for the final Kovaralloy layer: 12,700 microns, i.e., 0.5 inches.

[0062] By way of example, not to be considered limiting, the followingmetal combinations are believed suitable for seal-ring area 318 whenbonding the prepared sheet 304 to a Kovar alloy-nickel-gold frame 302(i.e., Kovar alloy core plated first with nickel and then with gold)using thermal compression (TC) bonding, or sonic, ultrasonic orthermosonic bonding.

EXAMPLE 1:

[0063] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.7 63.5

EXAMPLE 2:

[0064] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn or SnBi CVD, PVD, SBP 0.7 63.5

EXAMPLE 3:

[0065] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 4:

[0066] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Sn or Sn—Bi CVD, PVD, SBP0.7 63.5

EXAMPLE 5:

[0067] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn(de-stressed) CVD, PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD,PVD, SBP 0.002 6.35 4 Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 6:

[0068] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn—BiCVD, PVD 0.7 63.5

EXAMPLE 7:

[0069] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn or Sn—Bi CVD, PVD, SBP0.7 63.5

EXAMPLE 8:

[0070] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 9:

[0071] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Zn CVD, PVD, SBP 0.0026.35 4 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 10:

[0072] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.002 152.4 2 Sn or Sn—Bi CVD, PVD, SBP 0.7 63.5

EXAMPLE 11:

[0073] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.002 152.4 2 Al CVD, PVD, SBP 0.7 63.5

EXAMPLE 12:

[0074] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.002 152.4 2 Zn CVD, PVD, SBP 0.002 6.35 3 Al CVD, PVD, SBP 0.763.5

EXAMPLE 13;

[0075] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn CVD,PVD 0.7 63.5

EXAMPLE 14:

[0076] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15

EXAMPLE 15:

[0077] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.002 152.4

EXAMPLE 16:

[0078] Layers Metal Deposition Min. (microns) Max. (microns) Sn—Bi CVD,PVD 0.7 63.5

[0079] By way of further example, not to be considered limiting, thefollowing metal combinations and thicknesses are preferred for seal-ringarea 318 when bonding the prepared sheet 304 to a Kovaralloy-nickel-gold frame 302 using thermal compression (TC) bonding, orsonic, ultrasonic or thermosonic bonding.

Example 17:

[0080] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 1 50.8

Example 18:

[0081] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 Snor SnBi CVD, PVD, SBP 1 50.8

Example 19:

[0082] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 20:

[0083] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Sn or Sn—Bi CVD, PVD, SBP1 50.8

EXAMPLE 21:

[0084] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn(de-stressed) CVD, PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD,PVD, SBP 1 5.08 4 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 22:

[0085] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn—BiCVD, PVD 1 50.8

EXAMPLE 23:

[0086] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn or Sn—Bi CVD, PVD, SBP 150.8

EXAMPLE 24:

[0087] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Al CVD, PVD, SBP 1 50.8

EXAMPLE 25:

[0088] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Zn CVD, PVD, SBP 0.3175 5.08 4Al CVD, PVD, SBP 1 50.8

EXAMPLE 26:

[0089] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.1 5.08 2 Sn or Sn—Bi CVD, PVD, SBP 1 50.8

EXAMPLE 27:

[0090] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.1 5.08 2 Al CVD, PVD, SBP 1 50.8

EXAMPLE 28:

[0091] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.1 5.08 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Al CVD, PVD, SBP 1 50.8

EXAMPLE 29:

[0092] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn CVD,PVD 1 50.8

EXAMPLE 30

[0093] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12

EXAMPLE 31:

[0094] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.1 50.8

EXAMPLE 32:

[0095] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn—BiCVD, PVD 1 50.8

[0096] As indicated above, the previous examples are believed suitablefor application of, among other processes, thermal compression bonding.TC bonding is a process of diffusion bonding in which two preparedsurfaces are brought into intimate contact, and plastic deformation isinduced by the combined effect of pressure and temperature, which inturn results in atom movement causing the development of a crystallattice bridging the gap between facing surfaces and resulting inbonding. TC bonding takes place at significantly lower temperatures thanmany other forms of bonding such as braze soldering.

[0097] Referring now to FIG. 7, there is illustrated across-sectionalview of the prefabricated frame 302 suitable for use in this embodiment.The illustrated frame 302 includes a Kovar alloy core 702 overlaid witha first metallic layer 704 of nickel which, in turn, is overlaid by anouter layer 706 of gold. The use of Kovar alloy for the core 702 of theframe 302 is preferred where hard glass, e.g., Corning 7056 or 7058, isused for the sheet 304 and where Kovar alloy or a similar material isused for the package base 104, since these materials have a CTE for thetemperature range 30° C. to 300° C. that is within the range from about5.0·10⁻⁶/° K. to about 5.6·10⁻⁶/° K. (e.g. from about 5.0 to about 5.6ppm/° K.).

[0098] Referring still to FIG. 7, another step of the manufacturingprocess is the preparation of a prefabricated frame 302 for joining tothe sheet 304. As previously described, the frame 302 includes acontinuous sidewall 306 which defines an aperture 308 therethrough. Thesidewall 306 includes a frame seal-ring area 310 on its upper surfaceand a base seal-ring area 320 on its lower surface. The frame seal-ringarea 310 is generally dimensioned to conform with the sheet seal-ringarea 318 of the transparent sheet 304, while the base seal-ring area 320is dimensioned to conform against the corresponding seal area on thepackage base. The frame 302 may be manufactured using variousconventional metal forming technologies, including stamping, casting,die casting, extrusion/parting, and machining. It is contemplated thatstamping or die casting will be the most cost effective method forproducing the frames 302. Depending upon the degree of flatness requiredfor the contemplated bonding procedure and the degree achieved by aparticular frame manufacturing method, surface grinding, and possiblyeven lapping or polishing, may be required on the frame seal-ring area310 or base seal-ring area 320, to provide the final flatness necessaryfor a successful hermetic seal.

[0099] In this example, the base seal-ring area 320 is on the frame faceopposite frame seal-ring area 310, and utilizes the same layers ofnickel 704 overlaid by gold 706 to facilitate eventual welding to thepackage base 104.

[0100] It is important for the frame 302 to serve as a “heat sink” and“heat spreader” when the cover assembly 300 is eventually welded to thepackage base 104. It is contemplated that conventional high temperaturewelding processes (e.g., automatic resistance seam welding or laserwelding) will be used for this operation. If the metallized glass sheet304 was welded directly to the package base 104 using these weldingprocesses, the concentrated heat would cause thermal stresses likely tocrack the glass sheet or distort its optical properties. However, when ametal frame is attached to the transparent sheet, it acts as both a heatsink, absorbing some of the heat of welding, and as a heat spreader,distributing the heat over a wider area such that the thermal stress onthe transparent sheet 304 is reduced to minimize the likelihood ofcracking or optical distortion. Kovar alloy is especially useful in thisheat sink and heat spreading role as explained by Kovar alloy's thermalconductivity, 0.0395, which is approximately fourteen times higher thanthe thermal conductivity of Corning 7052 glass, 0.0028.

[0101] Another important aspect of the frame 302 is that it must beformed from a material having a CTE that is similar to the CTE of thetransparent sheet 304 and the CTE of the package base 104. This matchingof CTE between the frame 302, transparent sheet 304 and package base 104is required to minimize stresses between these components after they arejoined to one another so as to ensure the long term reliability of thehermetic seal therebetween under conditions of thermal cycling and/orthermal shock environments.

[0102] For window assemblies that will be attached to package basesformed of ceramic, alumina or Kovar alloy, Kovar alloy is preferred foruse as the material for the frame 304. Although Kovar alloy will be usedfor the frames in many of the embodiments discussed in detail herein, itwill be understood that Kovar alloy is not necessarily suitable for usewith all transparent sheet materials. Additionally, other framematerials besides Kovar alloy may be suitable for use with glass.Suitability is determined by the necessity that the material of thetransparent sheet 304, the material of the frame 302 and the material ofthe package base 104 all have closely matching CTEs to insure maximumlong-term reliability of the hermetic seals.

[0103] Referring now to FIG. 8, the next step of the manufacturingprocess is to position the frame 302 against the sheet 304 such that atleast a portion of the frame seal-ring area 310 and a least a portion ofthe sheet seal-ring area 318 contact one another along a continuousjunction region 804 that circumscribes the window portion 312. Actually,in some cases a plasma-cleaning operation is performed on the seal-ringareas and any other sealing surfaces just prior to joining thecomponents to ensure maximum reliability of the joint. In FIG. 8, thesheet 304 moves from its original position (denoted in broken lines)until it is in contact with the frame 302. It is, of course, firstnecessary to remove any remaining tacky tape or other masking materialsleft over from operations used to prepare the sheet seal-ring area 318if they cannot with stand the elevated temperatures encountered in thejoining process without degradation of the mask material and/or itsadhesive, if an adhesive is used to attach the mask to the sheet. Itwill be appreciated that it is not necessary that the sheet seal-ringarea 318 and the frame seal-ring area 310 have an exact correspondencewith regard to their entire areas, rather, it is only necessary thatthere be some correspondence between the two seal-ring areas forming acontinuous junction region 804 which circumscribes the window portion312. In the embodiment illustrated in FIG. 8, the metallized layers 610in the sheet seal-ring area 318 are much wider than the plated outerlayer 706 of the frame seal-ring area 310. Further, the window portion312 of the sheet 304 extends partway through the frame aperture 308,providing a means to center the sheet 304 on the frame 302.

[0104] The next step of the manufacturing process is to heat thejunction region 804 until a metal-to-metal joint is formed between theframe 302 and the sheet 304 all along the junction region, whereby ahermetic seal circumscribing the window portion 312 is formed. It isnecessary that during the step of heating the junction region 804, thetemperature of the window portion 312 of the sheet 304 remain below itsglass transition temperature, T_(G) to prevent damage to the finishedsurfaces 314 and 316. The current invention contemplates several optionsfor accomplishing this heating. A first option is to utilize thermalcompression (TC) bonding. As previously described, TC bonding involvesthe application of high pressures to the materials being joined suchthat a reduced temperature is required to produce the necessarydiffusion bond. Rules for determining the thickness and composition ofthe metallic layers 610 on the sheet 304 were previously provided, forTC bonding to, e.g., a Kovar alloy, nickel or gold frame such asillustrated in FIG. 7. The estimated process parameters for the TCbonding of a Kovar alloy/nickel/gold frame 302 to a metallized sheet 304having aluminum as the final layer would be a temperature ofapproximately 380° C. at an applied pressure of approximately 95,500psi. Under these conditions, the gold plating 706 on the Kovar alloyframe 302 will diffuse into/with the aluminum layer, e.g., layer 4 inExample 7. Since the 380° C. temperature necessary for TC bonding isbelow the approximately 500° C. to 900° C. T_(G) for hard glasses suchas Corning 7056, the TC bonding process could be performed in a singleor batch mode by fixturing the cover assembly components 302, 304together in compression and placing the compressed assemblies into afurnace (or oven, etc.) at approximately 380° C. The hermetic bond wouldbe obtained without risking the finished surfaces 314 and 316 of thewindow portion 312.

[0105] Alternatively, employing resistance welding at the junction area804 to add additional heat in addition to the TC bonding could allowpreheating the window assemblies to less than 380° C. and possiblyreduce the overall bonding process time. In another method, the TCbonding could be accomplished by fixturing the cover assembly components302 and 304 using heated tooling that would heat the junction area 304by conduction. In yet another alternative method, resistance welding canbe used to supply 100% of the heat required to achieve the necessary TCbonding temperature, thereby eliminating the need for furnaces, ovens,etc. or specialized thermally conductive tooling.

[0106] After completion of TC bonding or other welding processes, thewindow assembly 300 is ready for final processing, for example,chamfering the edges of the cover assembly to smooth them and preventchipping, scratching, marking, etc., during post-assembly, cleaning,marking or other operations.

[0107] Referring now to FIG. 9, there is illustrated a block diagram ofthe manufacturing process just described in accordance with oneembodiment of the current invention. Block 902 represents the step ofobtaining a sheet of transparent material, e.g., glass or othermaterial, having finished top and bottom surfaces as previouslydescribed. The process then proceeds to block 904 as indicated by thearrow.

[0108] Block 904 represents the step of applying surface treatments tothe sheet, e.g., scratch-resistant or anti-reflective coatings, aspreviously described. In addition to these permanent surface treatments,block 904 also represents the sub-steps of applying tape or othertemporary masks to the surfaces of the sheet to protect them during thesubsequent steps of the process. It will be appreciated that the stepsrepresented by block 904 are optional and that one or more of thesesteps may not be present in every embodiment of the invention. Theprocess then proceeds to block 906 as indicated by the arrow.

[0109] Block 906 represents the step of preparing the seal-ring area onthe sheet to provide better adhesion for the required metallic layers.This step usually involves roughening the seal-ring area using chemicaletching, mechanical grinding, laser ablating or sandblasting aspreviously described. To the extent necessary, block 906 also representsthe sub-steps of removing any masking material from the seal-ring area.It will be appreciated that the steps represented by block 906 areoptional and that some or all of these steps may not be present in everyembodiment of the invention. The process then proceeds to block 908 asindicated by the arrow.

[0110] Block 908 represents the step of metallizing the seal-ring areasof the sheet. The step represented by block 908 is mandatory since atleast one metallic layer must be applied to the seal-ring area of thesheet. In most embodiments, block 908 will represent numerous sub-stepsfor applying successive metallic layers to the sheet, where the layersof each sub-step may be applied by processes including CVD, PVD,cold-spray or solution bath plating as previously described. Followingthe steps represented by block 908, the sheet is ready for joining tothe frame. However, before the process can proceed to this joining step(i.e., block 916), a suitable frame must first be prepared.

[0111] Block 910 represents the step of obtaining a pre-fabricated framehaving a CTE that closely matches the CTE of the transparent sheet fromblock 902 and the CTE of the package base. In most cases where the baseis alumina or Kovar alloy, a frame formed of Kovar alloy will besuitable. As previously described, the frame may be formed using, e.g.,stamping, die-casting or other known metal-forming processes. Theprocess then proceeds to block 912 as indicated by the arrow.

[0112] Block 912 represents the step of grinding, polishing and/orotherwise flattening the seal-ring areas of the frame as necessary toincrease its flatness so that it will fit closely against the seal-ringareas of the transparent sheet. It will be appreciated that the stepsrepresented by block 912 are optional and may not be necessary orpresent in every embodiment of the invention. The process then proceedsto block 914 as indicated by the arrow.

[0113] Block 914 represents the step of applying additional metalliclayers to the seal-ring areas of the frame. These metallic layers arefrequently necessary to achieve compatible chemistry for bonding withthe metallized seal-ring areas of the transparent sheet. In mostembodiments, block 914 will represent numerous sub-steps for applyingsuccessive metallic layers to the frame. Once the steps represented byblock 914 are completed, the frame is ready for joining to thetransparent sheet. Thus, the results of process block 908 and block 914both proceed to block 916 as indicated by the arrows.

[0114] Block 916 represents the step of clamping the prepared frametogether with the prepared transparent sheet so that their respectivemetallized seal-ring areas are in contact with one another underconditions producing a predetermined contact pressure at the junctionregion circumscribing the window portion. This predetermined contactpressure between the seal-ring surfaces allows thermal compression (TC)bonding of the metallized surfaces to occur at a lower temperature thanwould be required for conventional welding (including most soldering andbrazing processes). The process then proceeds to block 918 as indicatedby the arrow.

[0115] Block 918 represents the step of applying heat to the junctionbetween the frame and the transparent sheet while maintaining thepredetermined contact pressure until the temperature is sufficient tocause thermal compression bonding to occur. In some embodiments, block918 will represent a single heating step, e.g., heating the fixturedassembly in a furnace. In other embodiments, block 918 will representseveral sub-steps for applying heat to the junction area, for example,first preheating the fixtured assembly (e.g., in a furnace) to anintermediate temperature, and then using resistance welding techniquesalong the junction to raise the temperature of the localized area of themetallic layers the rest of the way to the temperature where thermalcompression bonding will occur. The thermal compression bonding createsa hermetic seal between the transparent sheet material and the frame.The process then proceeds to block 920 as indicated by the arrow.

[0116] Block 920 represents the step of completing the window assembly.Block 920 may represent merely cooling the window assembly after thermalcompression bonding, or it may represent additional finishing processesincluding chamfering the edges of the assembly to prevent chipping,cracking, etc., marking the assembly, or other post-assembly procedures.The process of this embodiment has thus been described.

[0117] It will be appreciated that in alternative embodiments of theinvention, conventional welding techniques (including soldering and/orbrazing) may be used instead of thermal compression bonding to join theframe to the transparent sheet. In such alternative embodiments, thesteps represented by blocks 916 and 918 of FIG. 9 would be replaced bythe steps of fixturing the frame and transparent sheet together so thatthe metallized seal-ring areas are in contact with one another (but notnecessarily producing a predetermined contact pressure along thejunction) and then applying heat to the junction area using conventionalmeans until the temperature is sufficient to cause the melting anddiffusing of the metallic layers necessary to achieve the welded bond.

[0118] In an alternative embodiment, braze-soldering is used to join theframe 302 to the metallized sheet 304. In this embodiment, a soldermetal or solder alloy is utilized as the final layer of the metalliclayers 610 on the metallized sheet 304, and clamping the sheet 304 tothe frame 302 at a high predetermined contact pressure is not required.Light to moderate clamping pressure can be used: 1) to insure alignmentduring the solder's molten phase; and 2) to promote even distribution ofthe molten solder all along the junction region between the respectiveseal-ring areas; thereby helping to insure a hermetic seal, however,this clamping pressure does not contribute to the bonding process itselfas in TC bonding. In most other respects, however, this embodiment issubstantially similar to that previously described.

[0119] The following examples, not to be considered limiting, areprovided to illustrate the details of the metallic layers 610 in thesheet seal-ring area 318 that are suitable for braze-soldering to aKovar alloy/nickel/gold frame 302 such as that illustrated in FIG. 7.

EXAMPLE 33:

[0120] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 34:

[0121] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 35:

[0122] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 36:

[0123] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 37:

[0124] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.0026.35 4 Eutectic Au—Sn CVD, PVD, SBP 1.27 127 solder

EXAMPLE 38:

[0125] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Eutectic Au—Sn CVD, PVD,SBP 1.27 127 solder

EXAMPLE 39:

[0126] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.0026.35 4 Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 40:

[0127] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn—Bi solder CVD, PVD,SBP 1.27 152.4

EXAMPLE 41:

[0128] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.002 0.15 2 Sn—Bi solder CVD, PVD, SBP 1.27 152.4

EXAMPLE 42:

[0129] Layers Metal Deposition Min. (microns) Max. (microns) 1De-stressed Sn CVD, PVD 1.27 152.4 Solder

EXAMPLE 43:

[0130] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn—BiSolder CVD, PVD 1.27 152.4

EXAMPLE 44:

[0131] Min. Max. Layers Metal Deposition (microns) (microns) 1 EutecticAu—Sn CVD, PVD 1.27 127 Solder

EXAMPLE 45:

[0132] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.002 152.4 2 Eutectic Au—Sn CVD, PVD, SBP 1.27 127 Solder

EXAMPLE 46:

[0133] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.002 152.4 2 Sn—Bi Solder CVD, PVD, SBP 1.27 152.4

[0134] By way of further examples, not to be considered limiting, thefollowing combinations are preferred for the metallic layers 610 in thesheet seal-ring area 318 for braze-soldering to a Kovaralloy/nickel/gold frame 302 such as that illustrated in FIG. 7.

EXAMPLE 47:

[0135] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 48:

[0136] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 49:

[0137] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 50:

[0138] Min. Max. Layers Metal Deposition (microns) (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 51:

[0139] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5 solder

EXAMPLE 52:

[0140] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Eutectic Au—Sn CVD, PVD, SBP2.54 63.5 solder

EXAMPLE 53:

[0141] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 54:

[0142] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn—Bi solder CVD, PVD, SBP2.54 127

EXAMPLE 55:

[0143] Min. Max. Layers Metal Deposition (microns) (microns) 1 Cr CVD,PVD 0.05 0.12 2 Sn—Bi solder CVD, PVD, SBP 2.54 127

EXAMPLE 56:

[0144] Layers Metal Deposition Min. (microns) Max. (microns) 1De-stressed Sn CVD, PVD 2.54 127 Solder

EXAMPLE 57:

[0145] Layers Metal Deposition Min. (microns) Max. (microns) 1 Sn—BiSolder CVD, PVD 2.54 127

EXAMPLE 58:

[0146] Min. Max. Layers Metal Deposition (microns) (microns) 1 EutecticAu—Sn CVD, PVD 2.54 63.5 Solder

EXAMPLE 59:

[0147] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.1 5.08 2 Eutectic Au—Sn CVD, PVD, SBP 2.54 63.5 Solder

EXAMPLE 60:

[0148] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.1 5.08 2 Sn—Bi Solder CVD, PVD, SBP 2.54 127

[0149] Referring now to FIG. 10, there is illustrated yet anotherembodiment of the current invention. Note that in this embodiment, thecover assembly 300 is circular in configuration rather than rectangular.It will be appreciated that this is simply another possibleconfiguration for a cover assembly manufactured in accordance with thisinvention, and that this embodiment is not limited to configurations ofany particular shape. As in the embodiment previously described, thisembodiment also uses braze-soldering to hermetically join thetransparent sheet 304 to the frame 302. However, in this embodiment, thesolder is provided in the form of a separate solder preform 1000 havingthe shape of the sheet seal-ring area 318 or the frame seal-ring area310.

[0150] In this embodiment, instead of positioning the frame and thesheet directly against one another, the frame 302 and the sheet 304 areinstead positioned against opposite sides of the solder preform 1000such that the solder preform is interposed between the frame seal-ringarea 310 and the sheet seal-ring are 318 along a continuous junctionregion that circumscribes the window portion 312. After the frame 302and sheet 304 are positioned against the solder preform 1000, thejunction region is heated until the solder preform fuses forming asolder joint between the frame and sheet all along the junction region.The heating of the junction region may be performed by any of theprocedures previously described, including heating or preheating in afurnace, oven, etc., either alone or in combination with other heatingmethods including resistance welding. It is required that during thestep of heating the junction region, the temperature of the windowportion 312 of the sheet 304 remain below the glass transitiontemperature T_(G) such that the finished surfaces 314 and 316 on thesheet are not adversely affected.

[0151] The current embodiment using a solder preform 1000 can be usedfor joining a metallized sheet 304 to a Kovar alloy/nickel/gold framesuch as that illustrated in FIG. 7. In accordance with a preferredembodiment, the solder preform 1000 is formed of a gold-tin (Au—Sn)alloy, and in a more preferred embodiment, the gold-tin alloy is theeutectic composition. The thickness of the gold-tin preform 1000 will bewithin the range from about 6 microns to about 101.2 microns.

[0152] The following examples, not to be considered limiting, areprovided to illustrate the details of the metallic layers 610 and thesheet seal-ring area 318 that are suitable for braze-soldering to aKovar alloy/nickel/gold frame in combination with a gold-tin solderpreform.

EXAMPLE 61:

[0153] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 62:

[0154] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.002 25 2 Cu CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 63:

[0155] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 64:

[0156] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.002 25 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.002 6.354 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 65:

[0157] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.0026.35 4 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 66:

[0158] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Au CVD, PVD, SBP 0.05080.508

EXAMPLE 67:

[0159] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Zn CVD, PVD, SBP 0.002 6.35 3 Ni CVD, PVD, SBP 0.0026.35 4 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 68:

[0160] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Ni CVD, PVD, SBP 0.002 6.35 3 Sn—Bi CVD, PVD, SBP 0.63512.7

EXAMPLE 69:

[0161] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15 2 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 70:

[0162] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.002 0.15

EXAMPLE 71:

[0163] Layers Metal Deposition Min. (microns) Max. (microns) 1De-stressed Sn CVD, PVD 0.635 12.7 or Sn—Bi

EXAMPLE 72:

[0164] Layers Metal Deposition Min. (microns) Max. (microns) 1 Au CVD,PVD 0.0508 0.508

EXAMPLE 73:

[0165] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.002 152.4 2 Au CVD, PVD, SBP 0.0508 0.508

EXAMPLE 74:

[0166] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.002 152.4 2 Sn—Bi CVD, PVD, SBP 0.635 12.7

EXAMPLE 75:

[0167] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.002 152.4 2 Sn (De-stressed CVD, PVD, SBP 0.635 12.7 afterdeposition)

[0168] By way of further examples, not to be considered limiting, thefollowing combinations are preferred for the metallic layers 610 and thesheet seal-ring area 318 for braze-soldering to a Kovaralloy/nickel/gold frame in combination with a gold-tin soldered preform.

EXAMPLE 76:

[0169] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4 AuCVD, PVD, SBP 0.127 0.381

EXAMPLE 77:

[0170] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.1 2.54 2 Cu CVD, PVD, SBP 0.25 2.54 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 78:

[0171] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 79:

[0172] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al CVD,PVD 0.1 2.54 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 80:

[0173] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 81:

[0174] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 82:

[0175] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Zn CVD, PVD, SBP 0.3175 5.08 3 Ni CVD, PVD, SBP 1 5.08 4Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 83:

[0176] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Ni CVD, PVD, SBP 1 5.08 3 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 84:

[0177] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12 2 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 85:

[0178] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr CVD,PVD 0.05 0.12

EXAMPLE 86:

[0179] Layers Metal Deposition Min. (microns) Max. (microns) 1De-stressed Sn CVD, PVD 2.54 7.62 or Sn—Bi

EXAMPLE 87:

[0180] Layers Metal Deposition Min. (microns) Max. (microns) 1 Au CVD,PVD 0.127 0.381

EXAMPLE 88:

[0181] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.1 5.08 2 Au CVD, PVD, SBP 0.127 0.381

EXAMPLE 89

[0182] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni CVD,PVD 0.1 5.08 2 Sn—Bi CVD, PVD, SBP 2.54 7.62

EXAMPLE 90:

[0183] Min. Max. Layers Metal Deposition (microns) (microns) 1 Ni CVD,PVD 0.1 5.08 2 Sn (De-stressed CVD, PVD, SBP 2.54 7.62 after deposition)

[0184] Referring now to FIG. 11, there is illustrated yet anotherembodiment of the current invention. This embodiment also usessoldering, however, in this embodiment the solder is applied via inkjettechnology to either the metallized area 610 in the sheet seal-ring area318 or the sheet seal-ring 310 of the frame assembly. FIG. 11 shows aportion of the Kovar alloy/nickel/gold frame 302 and an inkjetdispensing head 1102 which is dispensing overlapping drops of solder1104 onto the frame seal-ring area 310 as the dispensing head movesaround the frame aperture 308 as indicated by arrow 1106. Preferably,the inkjet dispensed solder is a gold-tin (Au-Sn) alloy, and morepreferably it is the eutectic composition. The thickness of the gold-tinsolder applied by dispensing head 1102 in this embodiment is within therange from about 6 microns to about 101.2 microns. It will beappreciated that while the example illustrated in FIG. 11 shows thedispensing head 1102 depositing the solder droplets 1104 onto the frame302, in other embodiments the inkjet deposited solder may be applied tothe sheet seal-ring area 318, either alone or in combination withapplications on the frame seal-ring area 310. In still otherembodiments, the inkjet deposited solder may be used to create adiscrete solder preform that would be employed as described in theprevious examples herein. Details of the metallic layers 610 in thesheet seal-ring area 318 that are suitable for a soldering to a Kovaralloy/nickel/gold frame 302 such as that illustrated in FIG. 7 usinginkjet supplied solder are substantially identical to those layersillustrated in previous Examples 21 through 32.

[0185] Referring now to FIGS. 12a through 12 c and FIGS. 13a through 13c, there is illustrated yet another alternative method for manufacturingcover assemblies constituting another embodiment of the currentinvention. Whereas, in the previous embodiments a separate prefabricatedmetal frame was joined to the transparent sheet to act as a heatspreader/heat sink needed for subsequent welding, in this embodiment acold gas dynamic spray deposition process is used to fabricate ametallic frame/heat spreader directly on the transparent sheet material.In other words, in this embodiment the frame is fabricated directly onthe transparent sheet as an integral part, no subsequent joiningoperation is required. In addition, since cold gas dynamic spraydeposition can be accomplished at near room temperature, this method isespecially useful where the transparent sheet material and/or surfacetreatments thereto have a relatively low T_(G), melting temperature, orother heat tolerance parameter.

[0186] Referring specifically to FIG. 12a, there is illustrated a sheetof transparent material 304 having a window portion 312 definedthereupon. The window portion 312 has finished top and bottom surfaces314 and 316 (note that the 304 sheet appears bottom side up in FIGS. 12athrough 12 c). A frame attachment area 1200 is defined on the sheet 304,the frame attachment area circumscribing the window portion 312. It willbe appreciated in the embodiment illustrated in FIG. 12 that the frameattachment area 1200 need not follow the specific boundaries of thewindow area 312 (i.e., which in this case are circular) as long as theframe attachment area 1200 completely circumscribes the window portion.

[0187] It will be appreciated that, unless specifically noted otherwise,the initial steps of obtaining a transparent sheet having a windowportion with finished top and bottom surfaces, preparing the seal-ringarea of the sheet and metallizing the seal-ring area of the sheet aresubstantially identical to those described for the previous embodimentsand will not be described in detail again.

[0188] Referring now also to FIG. 13a, there is illustrated a partialcross-sectional view to the edge of the sheet 304. In this example, thestep of preparing a frame attachment area 1200 on the sheet 304comprises roughening the frame attachment area by roughening and/orgrinding the surface from its original level (shown in broken line) toproduce a recessed area 1302. After the frame attachment area 1200 hasbeen prepared, metal layers are deposited into the frame attachment areaof the sheet using cold gas dynamic spray deposition. In FIG. 12b, aninitial metal layer 1202 has been applied into the frame attachment area1200 using cold gas dynamic spray deposition.

[0189] Referring now also to FIG. 13b, the cold gas dynamic spray nozzle1304 is shown depositing a stream of metal particles 1306 onto the frameattachment area 1200. The initial layer 1202 has now been overlaid witha secondary layer 1204 and the spray nozzle 1304 is shown as it beginsto deposit the final Kovar alloy layer 1206.

[0190] Referring now to FIG. 12c, the completed cover assembly 1210 isillustrated including the integral frame/heat spreader 1212, which hasbeen built up from layer 1206 to a predetermined height, denoted byreference numeral 1308, above the finished surface of the sheet. In apreferred embodiment, the predetermined height 1308 of the built-upmetal frame above the frame attachment area 1200 is within the rangefrom about 5% to about 100% of the thickness denoted by referencenumeral 1310 of the sheet 304 beneath the frame attachment area. In theembodiment shown, the step of depositing metal using cold gas dynamicspray included depositing a layer of Kovar alloy onto the sheet tofabricate the built-up frame/heat spreader 1212. The use of cold gasdynamic spray deposition allows a tremendous range of thickness for thisKovar alloy layer, which thickness may be within the range from about2.54 microns to about 12,700 microns. It will, of course, be appreciatedthat the frame/heat spreader 1212 may be fabricated through thedeposition of materials other than Kovar alloy, depending upon thecharacteristics of the transparent sheet 304 and of the package base104, especially their respective CTEs.

[0191] The following examples, not to be considered limiting, areprovided to illustrate the details of the metallic layers, denotedcollectively by reference numeral 1207 for forming a frame/heat spreadercompatible with hard glass transparent sheets and Kovar alloy or ceramicpackage bases.

EXAMPLE 91

[0192] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 2.54 127 2 Cu cold gas spray 2.54 127 3 Ni cold gas spray 2.54127 4 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 92:

[0193] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar Alloy cold gasspray 127 12,700

EXAMPLE 93:

[0194] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 2.54 127 2 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 94:

[0195] Layers Metal Deposition Min. (microns) Max. (microns) 1 KovarAlloy cold gas spray 127 12,700

EXAMPLE 95:

[0196] Layers Metal Deposition Min. (microns) Max. (microns) 1 Zn coldgas spray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar alloy cold gasspray 127 12,700

EXAMPLE 96:

[0197] Layers Metal Deposition Min. (microns) Max. (microns) 1 Zn coldgas spray 2.54 127 2 Kovar alloy cold gas spray 127 12,700

EXAMPLE 97:

[0198] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr coldgas spray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar alloy cold gasspray 127 12,700

EXAMPLE 98:

[0199] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr coldgas spray 2.54 127 2 Kovar alloy cold gas spray 127 12,700

EXAMPLE 99:

[0200] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 2.54 127 2 Zn cold gas spray 2.54 127 3 Ni cold gas spray 2.54127 4 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 100:

[0201] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni coldgas spray 2.54 127 2 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 101:

[0202] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn orSn—Bi cold gas spray 2.54 127 2 Zn cold gas spray 2.54 127 3 Ni cold gasspray 2.54 127 4 Kovar Alloy cold gas spray 127 12,700

EXAMPLE 102:

[0203] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn orSn—Bi cold gas spray 2.54 127 2 Ni cold gas spray 2.54 127 3 Kovar Alloycold gas spray 127 12,700

[0204] By way of further examples, not to be considered limiting, thefollowing combinations are preferred for the metallic layers 1207 forforming a frame/heat spreader compatible with hard glass transparentsheets and Kovar alloy or ceramic package bases.

EXAMPLE 103:

[0205] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 12.7 76.2 2 Cu cold gas spray 12.7 76.2 3 Ni cold gas spray12.7 76.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 104:

[0206] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar Alloy cold gasspray 635 2,540

EXAMPLE 105:

[0207] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 12.7 76.2 2 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 106:

[0208] Layers Metal Deposition Min. (microns) Max. (microns) 1 KovarAlloy cold gas spray 635 2,540

EXAMPLE 107:

[0209] Layers Metal Deposition Min. (microns) Max. (microns) 1 Zn coldgas spray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar alloy cold gasspray 635 2,540

EXAMPLE 108:

[0210] Layers Metal Deposition Min. (microns) Max. (microns) 1 Zn coldgas spray 12.7 76.2 2 Kovar alloy cold gas spray 635 2,540

EXAMPLE 109:

[0211] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr coldgas spray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 Kovar alloy cold gasspray 635 2,540

EXAMPLE 110:

[0212] Layers Metal Deposition Min. (microns) Max. (microns) 1 Cr coldgas spray 12.7 76.2 2 Kovar alloy cold gas spray 635 2,540

EXAMPLE 111:

[0213] Layers Metal Deposition Min. (microns) Max. (microns) 1 Al coldgas spray 12.7 76.2 2 Zn cold gas spray 12.7 76.2 3 Ni cold gas spray12.7 76.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 112:

[0214] Layers Metal Deposition Min. (microns) Max. (microns) 1 Ni coldgas spray 12.7 76.2 2 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 113:

[0215] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn orSn—Bi cold gas spray 12.7 76.2 2 Zn cold gas spray 12.7 76.2 3 Ni coldgas spray 12.7 76.2 4 Kovar Alloy cold gas spray 635 2,540

EXAMPLE 114:

[0216] Min. Max. Layers Metal Deposition (microns) (microns) 1 Sn orSn—Bi cold gas spray 12.7 76.2 2 Ni cold gas spray 12.7 76.2 3 KovarAlloy cold gas spray 635 2,540

[0217] After the deposition of the metal layers using the cold gasdynamic spray deposition, it may be necessary to grind or shape the topsurface of the built-up frame 1212 to a predetermined flatness beforeperforming additional steps to ensure that a good contact will be madein later bonding. Another process which may be used, either alone or incombination with shaping the top surface of the built-up frame, is thedepositing of additional metal layers onto the built-up frame/heatspreader 1212 using solution bath plating. The most common reason forsuch plated layers is to promote a good bonding when the frame/heatspreader is adjoined to the package base 104. In a preferred embodiment,the additional metallic layers applied to the built-up frame 1212include a layer of nickel directly over the cold gas dynamic spraydeposited metal having a thickness within the range of about 0.002microns to about 25 microns and then solution bath plating a layer ofgold over the nickel layer until the gold layer has a thickness withinthe range from about 0.0508 microns to about 0.508 microns.

[0218] Referring now to FIG. 14, there is illustrated a block diagram ofthe alternative embodiment utilizing cold gas dynamic spray deposition.It will be appreciated that, unless specifically noted otherwise, theinitial steps of obtaining a transparent sheet having finished surfaces,applying surface treatments to the sheet, cleaning, roughening orotherwise preparing the frame attachment area of the sheet aresubstantially identical to those described for the previous embodimentsand will not be described in detail again. For example, block 1402 ofFIG. 14 represents the step of obtaining a sheet of transparent materialhaving finished surfaces and corresponds directly with block 902, andwith the description of suitable transparent materials. Similarly,except as noted, blocks 1404, 1406 and 1408 of FIG. 14 corresponddirectly with blocks 904, 906 and 908, respectively, of FIG. 9 and withthe previous descriptions of the steps and sub-steps provided herein.Thus, it will be understood that all of the options described forperforming the various steps and sub-steps represented by the blocks902-908 in the previous (i.e., prefabricated frame) embodiments areapplicable to the blocks 1402-1408 in the current (i.e., cold spray)embodiment.

[0219] The next step of the process is to use cold gas dynamic spraydeposition to deposit frame/heat spreader metal onto any previouslydeposited metal layers in the frame attachment area 1200. This step isrepresented by block 1410. As previously described in connection withFIGS. 13b and 13 c, the high velocity particles 1306 from the gas nozzle1304 form a new layer on the previous metallic layers, and by directingthe cold spray jet across the frame attachment area 1200 repeatedly, thenew material can become a continuous metallic layer around the entireperiphery of the frame attachment area, i.e., it will circumscribe thewindow portion 312 of the transparent sheet 304. Where the material ofthe package base 104 (to which the cover assembly 1210 will eventuallybe joined) is Kovar alloy or appropriately metallized alumina, Kovaralloy is preferred for the material 1206 to be cold sprayed to form theintegral frame. In other cases, a heat spreader material must beselected which has a CTE that is closely matched to the CTE of thepackage base 104. Of course, that material must also be compatible withthe cold gas dynamic spray process.

[0220] The cold spraying of the powdered heat spreader material iscontinued until the new layer 1206 reaches the thickness required toserve as a heat spreader/integral frame. This would represent the end ofthe process represented by block 1410. For some applications, thebuilt-up heat spreader/frame 1212 is now complete and ready for use. Forother applications, however, performing further finishing operations onthe heat spreader/frame 1212 may be desirable.

[0221] For example, it is known that significant residual stresses maybe encountered in metal structures deposited using cold-gas dynamicspray technology as a result of the mechanics of the spray process.These stresses may make the resulting structure prone to dimensionalchanges, cracking or other stress-related problems during later use.Annealing by controlled heating and cooling is known to reduce oreliminate residual stresses. Thus, in some applications, the integralheat spreader/frame 1212 is annealed following its deposition on thesheet 304. This optional step is represented by block 1411 in FIG. 14.In some embodiments, the annealing step 1411 may include the annealingof the totality of the sprayed-on metals and alloys constituting theheat spreader/frame 1212. In other embodiments, however, the annealingstep 1411 includes annealing only the outermost portions of the integralbuilt-up heat spreader/frame 1212, while the inner layers are leftunannealed.

[0222] It will be appreciated that there are flatness requirements forthe sealing surface at the “top” of the heat spreader (which is actuallyprojecting from the bottom surface 316 of the sheet). If these flatnessrequirements are not met via the application of the heat spreadermaterial by the cold spray process, it will be necessary to flatten thesealing surface at the next step of the process. This step isrepresented by block 1412 in FIG. 14. There are a number of options forachieving the required surface flatness. First, it is possible to removesurface material from the heat spreader to achieve the requiredflatness. This may be accomplished by conventional surface grinding, byother traditional mechanical means, or it may be accomplished by thelaser removal of high spots. Where material removal is used, care mustbe taken to avoid damaging the finished window surfaces 314 and 316during the material removal operations. Special fixturing and/or maskingof the window portion 312 may be required. Alternatively, if the coldspray deposited heat spreader 1212 is ductile enough, the surface may beflattened using a press operation, i.e., pressing the frame against aflat pattern. This would reduce the handling precautions as compared tousing a surface grinder or laser operations.

[0223] Finally, as previously described, in some embodiments additionalmetal layers are plated onto the integral frame/heat spreader 1212.These optional plating operations, such as solution bath plating layersof nickel and gold onto a Kovar alloy frame, are represented by block1414 in FIG. 14. In the embodiment shown in FIG. 14, the optionalplating operation 1414 is performed after the optional flatteningoperation 1412, which in turn is performed after the optional annealingoperation 1411. While such order is preferred, it will be appreciatedthat in other embodiments the order of the optional finishing steps1411, 1412 and 1414 may be rearranged. The primary considerations forthe ordering of these finishing steps is whether later steps will damagethe results of earlier steps. For example, it would be impractical toperform plating step 1414 before the flattening step 1412 if theflattening was to be carried out by grinding, while it might beacceptable if the flattening was to be carried out by pressing.

[0224] Referring now to FIGS. 15a and 15 b, there is illustrated amethod for manufacturing multiple cover assemblies simultaneously inaccordance with another embodiment of the current invention. Shown inFIG. 15a is an exploded view of a multi-unit assembly which can besubdivided after fabrication to produce individual cover assemblies. Themulti-unit assembly 1500 includes a frame 1502 and a sheet 1504 of atransparent material. The frame 1502 has sidewalls 1506 defining aplurality of frame apertures 1508 therethrough. Each frame aperture 1508is circumscribed by a continuous sidewall section having a frameseal-ring area 1510 (denoted by cross-hatching). Each frame seal-ringarea 1510 has a metallic surface, which may result from the inherentmaterial of the frame 1502 or it may result from metal layers which havebeen applied to the surface of the frame. In some embodiments, the frame1502 includes reduced cross-sectional thickness areas 1509 formed on theframe sidewalls 1506 between adjacent frame apertures 1508. FIG. 15bshows the bottom side of the frame 1502, to better illustrate thereduced cross-sectional thickness areas 1509 formed between eachaperture 1508. Also illustrated is the base seal-ring area 1520 (denotedby cross-hatching) which surrounds each aperture 1508 to allow joiningto the package bases 104.

[0225] Except for the details just described, the multiple-apertureframe 1502 of this embodiment shares material, fabrication and designdetails with the single aperture frame 302 previously described. In thisregard, a preferred embodiment of the frame 1502 is primarily formed ofKovar alloy or similar materials and more preferably, will have a Kovaralloy core with a surface layer of gold overlaying an intermediate layerof nickel as previously described.

[0226] The transparent sheet 1504 for the multi-unit assembly can beformed from any type of transparent material as previously discussed forsheet 304. In this embodiment, however, the sheet 1504 has a pluralityof window portions 1512 defined thereupon, with each window portionhaving finished top and bottom surface 1514 and 1516, respectively. Aplurality of sheet seal-ring areas 1518 are denoted by cross-hatchingsurrounding each window portion in FIG. 15a. With respect to thematerial of the sheet 1504, with respect to the finished configurationof the top and bottom surfaces 1514 and 1516, respectively, of eachwindow portion 1512, with respect to surface treatments, and/orcoatings, the sheet 1504 is substantially identical to the single windowportion sheet 304 previously discussed.

[0227] The next step of the process of manufacturing the multi-unitassembly 1500 is to prepare the sheet seal-ring areas 1518 formetallization. As noted earlier, each sheet seal-ring area 1518circumscribes a window portion of the sheet 1504. The sheet seal-ringareas 1508 typically have a configuration which closely matches theconfiguration of the frame seal-ring areas 1510 to which they willeventually be joined. It will be appreciated, however, that in somecases other considerations will affect the configuration of the framegrid, e.g., when electrical resistance heating is used to producebonding, then the seal-ring areas 1518 must be connected to form theappropriate circuits. The steps of preparing the sheet seal-ring areas1518 for metallization is substantially identical to the steps andoptions presented during discussion of preparing the frame seal-ringarea 310 on the single aperture frame 302. Thus, at a minimum, preparingthe sheet seal-ring area 1518 involves a thorough (e.g., plasma)cleaning to remove any contaminants from the surfaces and typically alsoinvolves roughening the seal-ring area by chemical etching, laserablating, mechanical grinding or sandblasting this area.

[0228] The step of metallizing the prepared sheet seal-ring areas 1510of the sheet 1502 are substantially identical to the steps described formetallizing the frame seal-ring area 310 on the single aperture frame302. For example, the metal layers shown in Examples 1 through 8 can beused in connection with thermal compression bonding, the metal layers ofExamples 9 through 20 can be used for soldering where the soldermaterial is plated onto the sheet as a final metallic layer, the metallayer configurations of Examples 21 through 32 can be used in connectionwith soldering in combination with a separate gold-tin of solder preformand also for soldering in connection with solders deposited or formedusing inkjet technology.

[0229] The next step of the process is to position the frame 1502against the sheet 1504 (it being understood that solder preforms orsolder layers would be interposed between the frame and the sheet) suchthat each of the window portions 1512 overlays one of the frameapertures 1508, and that for each such window portion/frame aperturecombination, at least a portion of the associated frame seal-ring area1510 and at least a portion of the associated sheet seal-ring area 1518contact one another along a continuous junction region thatcircumscribes the associated window portion. This operation is generallyanalogous to the steps of positioning the frame against the sheet in thesingle aperture embodiment previously described.

[0230] Referring now to FIG. 16a, there is illustrated the positioningof a multi-window sheet 1504 (in this case having window portions 1512with contoured surfaces) against a multi-aperture frame 1502 usingcompliant tooling in accordance with another embodiment. The complianttooling includes a compliant element 1650 and upper and lower supportplates 1652, 1654, respectively. The support plates 1652 and 1654receive compressive force, denoted by arrows 1656, at discrete locationsfrom tooling fixtures (not shown). The compliant member 1650 ispositioned between one of the support plates and the cover assemblypre-fab (i.e., frame 1502 and sheet 1504). The compliant member 1650yields elastically when a force is applied, and therefore can conform toirregular surfaces (such as the sheet 1504) while at the same timeapplying a distributed force against the irregular surface to insurethat the required contact pressure is achieved all along the frame/sheetjunction. Such compliant tooling can also be used to press a sheet orframe against the other member when the two members are not completelyflat, taking advantage of the inherent flexibility (even if small)present in all materials. In the illustrated example, the compliantmember 1650 is formed from a solid block of an elastomer material, e.g.,rubber, however in other embodiments the compliant member may also befabricated from discrete elements, e.g., springs.

[0231] The next step of the process is heating all of the junctionregions until a metal-to-metal joint is formed between the frame 1502and the sheet 1504 all along each junction region, thus creating themulti-unit assembly 1500 having a hermetic frame/sheet sealcircumscribing each window portion 1512. It will be appreciated that anyof the heating technologies previously described for joining the singleaperture frame 302 to the single sheet 304 are applicable to joining themulti-aperture frame 1502 to the corresponding multi-window sheet 1504.

[0232] Referring now to FIG. 16b, the final step of the current processis to divide the multi-unit assembly 1500 along each junction regionthat is common between two window portions 1512 taking care to preserveand maintain the hermetic seal circumscribing each window portion. Aplurality of individual cover assemblies are thereby produced. FIG. 16b,illustrates a side view of a multi-unit assembly 1500 following thehermetic bonding of the sheet 1504 to the frame 1502. Where the frame1502 includes reduced cross-sectional thickness areas 1509, the step ofdividing the multi-unit assembly may include scoring the frame along theback side of the reduced cross-sectional thickness area at the positionindicated by arrow 1602, preferably breaking through or substantiallyweakening the remaining frame material below area 1509, and alsosimultaneously scoring the sheet 1504 along a line vertically adjacentto area 1509, i.e., at the point indicated by arrow 1604, followed byflexing the assembly 1500, e.g., in the direction indicated by arrows1606 such that a fracture will propagate away from the score along line1608, thereby separating the assembly into two pieces. This procedurecan be repeated along each area of reduced cross-sectional thickness1509 until the multi-unit assembly 1500 has been completely subdividedinto single aperture cover assemblies that are substantially identicalto those produced by the earlier method described herein. In otherembodiments, instead of using the score-and-break method, the coverassemblies may be cut apart, preferably from the frame side along thepath indicated by arrow 1602 (i.e., between the window portions 1512),using mechanical cutting, laser, water jet or other parting technology.

[0233] Referring now to FIGS. 17a and 17 b, there is illustrated yetanother method for simultaneously manufacturing multiple coverassemblies. This method expands upon the cold gas dynamic spraytechnique used to build an integral frame/heat spreader directly uponthe transparent sheet material as previously illustrated in connectionwith FIGS. 12a through 12 c and FIGS. 13a through 13 c. As shown in FIG.17a, the process starts with a sheet of nonmetallic transparent material1704 having a plurality of window portions 1712 defined thereupon, eachwindow portion having finished top and bottom surfaces 1714 and 1716,respectively. The properties and characteristics of the transparentsheet 1704 are substantially identical to those in the embodimentspreviously discussed. The next step of the process involves preparing aplurality of frame attachment areas 1720 (denoted by the path of thebroken line surrounding each window portion 1712), each frame attachmentarea 1720 circumscribing one of the window portions 1712. As in previousembodiments, the step of preparing the frame attachment areas maycomprise cleaning, roughening, grinding or otherwise modifying the frameattachment areas in preparation for metallization.

[0234] The next step in this process is metallizing the prepared frameattachment areas on the sheet, i.e., this metallization may be performedusing a cold gas dynamic spray technology or where the layers arerelatively thin, using a CVD, physical vapor deposition or otherconventional metal deposition techniques. It will be appreciated thatthe primary purpose of this step is to apply metal layers necessary toobtain good adhesion to the transparent sheet 1704 and/or to meet themetallurgical requirements for corrosion prevention, etc.

[0235] Referring now to FIG. 17b, the next step of the process isdepositing metal onto the prepared/metallized frame attachment areas ofthe sheet 1704 using cold gas dynamic spray deposition techniques untila built-up metal frame 1722 is formed upon the sheet having a seal-ringarea 1726 that is a predetermined vertical thickness above the frameattachment areas, thus creating a multi-unit assembly having an inherenthermetic seal between the frame 1722 and the sheet 1704 circumscribingeach window portion 1712. In some embodiments, reduced cross-sectionalthickness areas 1724 are formed by selectively depositing the metalduring the cold spray deposition. In other embodiments, the reducedcross-sectional area sections 1724 may be formed following deposition ofthe frame/heat spreader 1722 through the use of grinding, cutting orother mechanical techniques such as laser ablation and water jet.

[0236] The next step of the process which, while not required isstrongly preferred, is to flatten, if necessary, the seal-ring area 1726of the sprayed-on frame 1722 to meet the flatness requirements forjoining it to the package base 104. This flattening can be accomplishedby mechanical means, e.g., grinding, lapping, polishing, etc., or byother techniques such as laser ablation.

[0237] The next step of the process, which, while not required, isstrongly preferred, is to add additional metallic layers, e.g., a nickellayer and preferably also a gold layer, to the seal-ring area 1726 ofthe sprayed-on frame 1722 to facilitate welding the cover assembly tothe package base 104. These metallic layers are preferably added using asolution bath plating process, e.g., solution bath plating, althoughother techniques may be used.

[0238] The next step of the process is dividing the multi-unit assembly1700 along each frame wall section common between two window portions1712 while, at the same time, preserving and maintaining the hermeticseal circumscribing each window portion. After dividing the multi-unit1700, a plurality of single aperture cover assemblies 1728 (shown inbroken line) will be produced, each one being substantially identical tothe single aperture cover assemblies produced using the method describedin FIGS. 12a through 12 c and FIGS. 13a through 13 c. All of theoptions, characteristics and techniques described for use in the singleunit cover assembly produced using cold gas dynamic spray technology areapplicable to this embodiment. It will be appreciated that certainoperations for example, the flattening of the frame and the plating ofthe frame with additional metallic layers, may be performed on themulti-unit assembly 1700, prior to separation of the individual units,or on the individual units after separation.

[0239] As previously described, heating the junction region between themetallized seal-ring area of the transparent sheet and the seal-ringarea of the frame is required for forming the hermetic sealtherebetween. Also as previously described, this heating may beaccomplished using a furnace, oven, or various electrical heatingtechniques, including electrical resistance heating (ERH). Referring nowto FIGS. 18a-18 c, there is illustrated methods of utilizing electricresistance heating to manufacture multiple cover assembliessimultaneously.

[0240] Referring first to FIG. 18a, there is illustrated a transparentsheet 1804 having a plurality of seal-ring areas 1818 laid out in arectangular arrangement around a plurality of window portions 1812.These seal-ring areas 1818 have been first prepared, and then metallizedwith one or more metal or metal alloy layers, as previously describedherein. The transparent sheet 1804 further includes an electrode portion1830 which has been metallized, but does not circumscribe any windowportions 1812. This electrode portion is electrically connected to themetallized seal-ring areas 1818 of the sheet. One or more electrode pads1832 may be provided on the electrode portion 1830 to receive electricalenergy from electrodes during the subsequent ERH procedure.

[0241] Referring now to FIG. 18b, there is illustrated a frame 1802having a plurality of sidewalls 1806 laid out in a rectangulararrangement around a plurality of frame apertures 1808. The apertures1808 are disposed so as to correspond with the positions of the windowportions 1812 of the sheet 1804, and the sidewalls 1806 are disposed sothat frame seal-ring areas 1810 (located thereupon) correspond with thepositions of the sheet seal-ring areas 1818 of the sheet. The frame ismetallic or metallized in order to facilitate joining as previouslydescribed herein. The frame 1802 further includes an electrode portion1834 that does not circumscribe any frame apertures 1808. This frameelectrode portion 1834 is positioned so as not to correspond to theposition of the sheet electrode portion 1830, and preferably is disposedon an opposing side of the sheet-window/frame-grid assembly (i.e., whenthe sheet is assembled against the frame). The frame electrode portion1834 is electrically connected to the metallized frame seal-ring areas1810. One or more electrode pads 1836 may be provided on the electrodeportion 1834 to receive electrical energy from electrodes during thesubsequent ERH procedure.

[0242] Referring now to FIG. 18c, the sheet 1804 is shown positionedagainst the frame 1802 in preparation for heating to produce thehermetic seal therebetween. If applicable, solder or a solder preformhas been positioned therebetween as previously described. It will beappreciated that when the transparent sheet 1804 is brought against theframe 1802, the metallized seal-ring areas 1818 on the lower surface ofthe sheet will be in electrical contact with the metallized seal-ringareas 1810 on the upper surface of the frame. However, the sheetelectrode portion 1830 and the frame electrode portion 1834 will not bein direct contact with one another, but instead will be electricallyconnected only through the metallized seal-ring areas 1818 and 1810 towhich they are, respectively, electrically connected. When an electricalpotential is applied from electrode pads 1832 to electrode pads 1836(denoted by the “+” and “−” symbols adjacent to the electrodes),electrical current flows through the junction region of the entiresheet-window/frame-grid assembly. This current flow produces electricalresistance heating (ERH) due to the resistance inherent in the metalliclayers. In some embodiments, this electrical resistance heating may besufficient, in and of itself, to result in TC bonding, soldering, orother hermetic seal formation between the sheet 1804 and the frame 1802in order to form a multi-unit assembly. In other embodiments, however,electrical resistance heating may be combined with other heating formssuch as furnace or oven pre-heating in order to supply the necessaryheat required for bonding to form the multi-unit assembly.

[0243] After bonding the sheet 1804 to the frame 1802 to form themulti-unit assembly, the sheet electrode portion 1830 and the frameelectrode portion 1834 can be cut away and discarded, having servedtheir function of providing electrical access for external electrodes(or other electrical supply members) to the metallized seal-ring areasof the sheet and frame, respectively. The removal of these “sacrificial”electrode portions 1830 and 1834 may occur before or during the “dicing”process step, i.e., the separating of the multi-unit assembly intoindividual cover assemblies. It will be appreciated that any of thetechnologies previously described herein for separating a multi-unitassembly into individual cover assemblies can be used for the dicingstep of separating a multi-unit assembly fabricated using ERH heating.

[0244] Where ERH is to be used for manufacturing multiple coverassemblies simultaneously, the configuration of thesheet-window/frame-grid array and/or the placement of the electrodesportions within the sheet-window/frame-grid array may be selected tomodify the flow of current through the junction region during heating.The primary type of modification is to even the flow of current throughthe various portions of the sheet-window/frame-grid during heating toproduce more even temperatures, i.e., to avoid “hot spots” or “coldspots.”

[0245] Referring now to FIGS. 19a-19 f, there are illustrated varioussheet-window/frame-grid configurations adapted for producing more eventemperatures during ERH. In each of FIGS. 19a-19 f, there is shown asheet-window/frame-grid array 1900 comprising a prepared, metallizedtransparent sheet 1904 overlying a prepared, metallic/metallized frame1902. The window portions of the sheet 1904 directly overlie the frameapertures of the frame 1902, and the metallized seal-ring areas of thesheet directly overlie the seal-ring areas of the frame (it will beappreciated that metallized portions of the sheet 1904 and the frame1902 appear coincident in these figures). Metallized electrode portionsformed on the transparent sheet 1904 are denoted by reference letters A,B, C and D. These electrode portions A, B, C and D are electricallyconnected to the adjoining sheet seal-ring areas of the sheet, but areelectrically insulated from one another by non-metallized areas 1906 ofthe sheet. An external electrode is applied to the top of themetallic/metallized frame (on the side opposite from the sheet) acrossthe area denoted by reference letter E. For bonding or soldering,electrical power is applied at the electrodes, e.g., one line toelectrodes A, B, C and D simultaneously, and the other line to electrodeE, or alternatively, one line in sequence to each of electrode A, B, Cand D, and the other line to electrode E. It will be appreciated thatmany other combinations of electrode powering are within the scope ofthe invention.

[0246] Referring to FIG. 19f, this embodiment illustrates asheet-window/frame-grid 1900 having a “shingle” configuration, i.e.,where the seal-ring areas between the window portions/frame apertures donot form continuous straight lines across the assembly array.Shingle-arrangement frame assemblies are more labor-intensive toseparate using scribe-and-break or cutting procedures. Separating suchassemblies requires that each row first be separated from the overallgrid, and then that individual cover assemblies be separated from therow by separate scribe-and-break or cutting operations. Nevertheless,use of shingle-arrangement assemblies may have benefits relating toheating using ERH techniques.

[0247] While the invention has been shown or described in a variety ofits forms, it should be apparent to those skilled in the art that it isnot limited to these embodiments, but is susceptible to various changeswithout departing from the scope of the invention.

What is claimed is:
 1. A method for manufacturing a cover assembly thatcan be joined to a micro-device package base to form a hermeticallysealed micro-device package, the cover assembly including a transparentwindow portion and a metallic frame, the method comprising the followingsteps: providing a sheet of a transparent material having a windowportion defined thereupon, the window portion having finished top andbottom surfaces; preparing a frame-attachment area on the sheet, theframe-attachment area circumscribing the window portion; spraying afirst quantity of powdered metal particles onto the preparedframe-attachment area of the sheet using a jet of gas, the gas being ata temperature below the fusing temperature of the metal particles, thejet of gas having a velocity sufficient to cause the metal particles tomerge with one another upon impact with the sheet and with one anotherso as to form an initial continuous metallic coating adhering to theframe-attachment area of the sheet; and applying successive quantitiesof powdered metal particles over the initial continuous metallic coatingusing the jet of gas so as to form a continuous built-up metallic frameincorporating the initial continuous metallic coating as its base andhaving an overall thickness that is a predetermined thickness.
 2. Amethod in accordance with claim 1, wherein the temperature of the jet ofgas is below the glass transition temperature (T_(G)) of the transparentmaterial of the sheet.
 3. A method in accordance with claim 1, whereinthe temperature of the jet of gas is below the temperature at which anycoatings and finishes previously applied to the sheet are degraded.
 4. Amethod in accordance with claim 1, wherein the temperature of the jet ofgas is less than about 380° C.
 5. A method in accordance with claim 4,wherein the temperature of the jet of gas is near room temperature.
 6. Amethod in accordance with claim 5, wherein the cover assembly iscompletely manufactured at near room temperature.
 7. A method inaccordance with claim 1, wherein the first quantity of powdered metalparticles has a composition which is a pure metal.
 8. A method inaccordance with claim 7, wherein the composition of the first quantityof powdered metal particles is one of aluminum, zinc, chromium, nickel,silver, gold and tin.
 9. A method in accordance with claim 7, wherein atleast one of the successive quantities of powdered metal particles has acomposition which is a metal alloy.
 10. A method in accordance withclaim 9, wherein the metal alloy is Kovar alloy.
 11. A method inaccordance with claim 9, wherein the metal alloy has a coefficient ofthermal expansion (CTE) matching the CTE of the transparent sheet.
 12. Amethod in accordance with claim 1, wherein the first quantity ofpowdered metal particles has a composition which is a metal alloy.
 13. Amethod in accordance with claim 12, wherein the metal alloy of the firstquantity of powdered metal particles is one of Kovar alloy andtin-bismuth alloy.
 14. A method in accordance with claim 1, wherein thecomposition of the first quantity of powdered metal particles and thecomposition of at least one of the successive quantities of powderedmetal particles are different from one another such that the built-upmetallic frame includes at least two discrete metallic layers havingdifferent compositions.
 15. A method in accordance with claim 14,wherein the predetermined thickness of the built-up metallic frame iswithin the range from about 130 microns to about 13,081 microns.
 16. Amethod in accordance with claim 15, wherein the predetermined thicknessof the built-up metallic frame is within the range from about 648microns to about 2,769 microns.
 17. A method in accordance with claim 1,wherein the predetermined thickness of the overall thickness of thebuilt-up metal frame above the frame-attachment area is within the rangefrom about 5% to about 100% of the thickness of the transparent materialbeneath the frame-attachment area.
 18. A method in accordance with claim1, wherein the predetermined thickness of the built-up metallic frame iswithin the range from about 130 microns to about 13,081 microns.
 19. Amethod in accordance with claim 1, wherein the resulting cover assemblyis suitable for joining to the package base by welding.
 20. A method inaccordance with claim 1, wherein the resulting cover assembly issuitable for joining to the package base by soldering.
 21. A method formanufacturing a cover assembly for a micro-device package, the methodcomprising the following steps: providing a sheet of a transparentmaterial having a window portion defined thereupon; spraying a firstquantity of powdered particles onto the sheet using a jet of gas, thegas being at a temperature below the fusing temperature of theparticles, the jet of gas having a velocity sufficient to cause theparticles to merge with one another upon impact with the sheet and withone another so as to form an initial continuous coating adhering to thesheet and circumscribing the window portion thereof; and applyingsuccessive quantities of powdered particles over the initial continuouscoating using the jet of gas so as to form a continuous built-up framecircumscribing the window portion and incorporating the initialcontinuous coating.
 22. A method in accordance with claim 21, whereinthe temperature of the jet of gas is below the glass transitiontemperature (T_(G)) of the transparent material of the sheet.
 23. Amethod in accordance with claim 21, wherein the temperature of the jetof gas is below the temperature at which any coatings and finishespreviously applied to the sheet are degraded.
 24. A method in accordancewith claim 21, wherein the powdered particles are metal.
 25. A method inaccordance with claim 21, wherein the powdered particles are a polymericmaterial.
 26. A method in accordance with claim 21, wherein the overallthickness of the built-up frame above the transparent material is withinthe range from about 5% to about 100% of the thickness of thetransparent material beneath the frame.
 27. A method in accordance withclaim 21, wherein the predetermined thickness of the built-up frame iswithin the range from about 130 microns to about 13,081 microns.
 28. Amethod in accordance with claim 21, wherein the built-up frame has acoefficient of thermal expansion (CTE) matching the CTE of thetransparent sheet.
 29. A cover assembly that can be joined to amicro-device package base to form a hermetically sealed micro-devicepackage, the cover assembly including: a sheet of a transparent materialhaving a window portion defined thereupon; and a built-up metallic frameadhering to the sheet and circumscribing the window portion, the framehaving been deposited onto the sheet by first spraying a first quantityof powdered metal particles onto a prepared frame-attachment area of thesheet using a jet of gas, the gas being at a temperature below thefusing temperature of the metal particles, and the j et of gas having avelocity sufficient to cause the metal particles to merge with oneanother upon impact with the sheet and with one another so as to form aninitial continuous metallic coating adhering to the frame-attachmentarea of the sheet, and then applying successive quantities of powderedmetal particles over the initial continuous metallic coating using thejet of gas so as to form the built-up metallic frame incorporating theinitial continuous metallic coating as its base and having an overallthickness that is a predetermined thickness.
 30. A cover assembly inaccordance with claim 29, wherein the temperature of the jet of gas isbelow the glass transition temperature (T_(G)) of the transparentmaterial of the sheet.
 31. A cover assembly in accordance with claim 29,wherein the temperature of the jet of gas is below the temperature atwhich any coatings and finishes previously applied to the sheet aredegraded.
 32. A cover assembly in accordance with claim 29, wherein thebuilt-up metallic frame includes at least two discrete metallic layershaving different compositions.
 33. A cover assembly in accordance withclaim 32, wherein the majority of the built-up metallic frame is formedof a metallic layer of Kovar alloy.
 34. A cover assembly in accordancewith claim 29, wherein the built-up metallic frame has a coefficient ofthermal expansion (CTE) matching the CTE of the transparent sheet.
 35. Acover assembly in accordance with claim 29, wherein the predeterminedthickness of the overall thickness of the built-up metal frame above theframe-attachment area is within the range from about 5% to about 100% ofthe thickness of the transparent material beneath the frame-attachmentarea.
 36. A cover assembly in accordance with claim 29, wherein thepredetermined thickness of the built-up metallic frame is within therange from about 130 microns to about 13,081 microns.
 37. A coverassembly in accordance with claim 29, wherein the cover assembly issuitable for joining to the package base by welding.
 38. A coverassembly in accordance with claim 29, wherein the resulting coverassembly is suitable for joining to the package base by soldering.
 39. Amicro-device module including: a package base; a micro-device supportedon the package base; and a cover assembly joined to the package base soas to encapsulate the micro-device in a hermetically sealed cavityformed between the cover assembly and the package base, the coverassembly including a sheet of a transparent material having a windowportion defined thereupon and a built-up metallic frame adhering to thesheet and circumscribing the window portion, the frame having beendeposited onto the sheet by first spraying a first quantity of powderedmetal particles onto the sheet using a jet of gas, the gas being at atemperature below the fusing temperature of the metal particles, and thejet of gas having a velocity sufficient to cause the metal particles tomerge with one another upon impact with the sheet and with one anotherso as to form an initial continuous metallic coating adhering to thesheet, and then applying successive quantities of powdered metalparticles over the initial continuous metallic coating using the jet ofgas so as to form the built-up metallic frame incorporating the initialcontinuous metallic coating as its base.
 40. A micro-device module inaccordance with claim 39, wherein the temperature of the jet of gas isbelow the glass transition temperature (T_(G)) of the transparentmaterial of the sheet.
 41. A micro-device module in accordance withclaim 39, wherein the temperature of the jet of gas is below thetemperature at which any coatings and finishes previously applied to thesheet are harmed.
 42. A method for manufacturing a cover assembly thatcan be joined to a micro-device package base to form a hermeticallysealed micro-device package, the cover assembly including a transparentwindow portion and a frame, the method comprising the following steps:providing a sheet of a transparent material having a window portiondefined thereupon; preparing a frame-attachment area on the sheet, theframe-attachment area circumscribing the window portion; depositingmetal onto the prepared frame-attachment area of the sheet usingcold-gas dynamic spray deposition until a built-up metal frame is formedupon the sheet having a predetermined thickness above theframe-attachment area.
 43. A method in accordance with claim 42, whereinthe step of preparing a frame-attachment area on the sheet furthercomprises roughening the surface of the sheet along a pathcircumscribing the window portion.
 44. A method in accordance with claim42, wherein the predetermined thickness of the built-up metal frameabove the frame-attachment area is within the range from about 5% toabout 100% of the thickness of the sheet beneath the frame-attachmentarea.
 45. A method in accordance with claim 42, wherein the step ofdepositing metal further comprises depositing a layer of Kovar alloyonto the sheet using cold-gas dynamic spray deposition until the layerhas a thickness of within the range from about 127 microns to about12,700 microns.
 46. A method in accordance with claim 45, wherein thestep of depositing metal further comprises depositing a first layer ofaluminum onto the prepared frame-attachment area of the sheet before theKovar alloy layer using cold-gas dynamic spray deposition until thefirst layer has a thickness within the range from about 2.54 microns toabout 127 microns.
 47. A method in accordance with claim 46, wherein thestep of depositing metal further comprises depositing an intermediatelayer of nickel after the aluminum layer and before the Kovar alloylayer using cold-gas dynamic spray deposition until the second layer hasa thickness within the range from about 2.54 microns to about 127microns.
 48. A method in accordance with claim 47, wherein the step ofdepositing metal further comprises depositing an intermediate layer ofcopper after the aluminum layer and before the nickel layer usingcold-gas dynamic spray deposition until the second layer has a thicknessof within the range from about 2.54 microns to about 127 microns.
 49. Amethod in accordance with claim 45, wherein the step of depositing metalfurther comprises depositing a first layer of zinc onto the preparedframe-attachment area of the sheet using cold-gas dynamic spraydeposition until the first layer has a thickness within the range fromabout 2.54 microns to about 127 microns.
 50. A method in accordance withclaim 49, wherein the step of depositing metal further comprisesdepositing an intermediate layer of nickel after the zinc layer andbefore the Kovar alloy layer using cold-gas dynamic spray depositionuntil the nickel layer has a thickness within the range from about 2.54microns to about
 127. 51. A method in accordance with claim 45, whereinthe step of depositing metal further comprises depositing a first layerof chromium onto the prepared frame-attachment area of the sheet usingcold-gas dynamic spray deposition until the first layer has a thicknesswithin the range from about 2.54 microns to about 127 microns.
 52. Amethod in accordance with claim 51, wherein the step of depositing metalfurther comprises depositing an intermediate layer of nickel after thechromium layer and before the Kovar alloy layer using cold-gas dynamicspray deposition until the second layer has a thickness within the rangefrom about 2.54 microns to about 127 microns.
 53. A method in accordancewith claim 42, further comprising the step of depositing additionalmetallic layers onto the built-up frame using solution bath plating. 54.A method in accordance with claim 53, further comprising the step offlattening the top surface of the built-up frame to a predeterminedflatness after the cold-gas dynamic spray metal deposition and beforedepositing additional metallic layers using solution bath plating.
 55. Amethod in accordance with claim 53, wherein the step of flattening thetop surface of the built-up frame is performed using one of grinding,lapping, pressing and laser ablation procedures.
 56. A method inaccordance with claim 53, wherein the step of depositing additionalmetallic layers using solution bath plating includes: plating a layer ofnickel over the cold-gas dynamic spray deposited metal of the frameuntil the nickel layer has a thickness within the range from about 0.002microns to about 25 microns; and plating a layer of gold over the nickellayer until the gold layer has a thickness within the range from about0.0508 microns to about 0.508 microns.
 57. A method in accordance withclaim 42, further comprising the step of annealing the built-up frame byheating after its deposition onto the sheet.
 58. A method in accordancewith claim 57, wherein the step of annealing includes annealing thetotality of the sprayed-on metals and alloys.
 59. A method in accordancewith claim 57, wherein the step of annealing includes annealing only theoutermost portions of the integral built-up frame.